Worldwide elimination of smallpox by vaccination with orthopox viruses such as vaccinia has validated the safety and efficacy of poxvirus vaccines. Today, poxviruses have a wide range of applications, in part because these viruses contain large genomes that can accommodate insertion of foreign DNA. For example, the vaccinia virus genome can tolerate insertions of up to 25,000 base pairs of foreign DNA (Smith and Moss, BioTechniques, 25(1):21-28, 1983). Thus, poxviruses are used to stimulate responses not only to poxviral antigens, but also to heterologous viral, bacterial, or tumor antigens with numerous prophylactic and therapeutic indications. In addition, poxviruses can be used to deliver any therapeutic DNA, such as a transgene encoding a therapeutic protein (e.g., a cytokine), into a subject. Production of virus stocks in vitro is preferable to propagation in animal hosts from a safety standpoint (Hruby, Clin. Microbio., 3(2): 153-170, 1990). However, large-scale commercial production can be hampered by the limited cell types such as primary cells to support virus production in vitro. Optimizing virus yield and quality in cell culture-based manufacturing methods will increase the commercial feasibility of therapeutic viral vectors.